The invention relates to a shifting device for a transmission unit of a vehicle operated by muscle force.
The invention also relates to a transmission unit for a vehicle operated muscle force.
The invention additionally relates to a transmission housing for a transmission unit of a vehicle driven by muscle force.
Such transmission units serve to step up or step down the muscle force and as a result the provision of driving force to the vehicle.
Basically, there are three types of gearshifts for vehicles or motorbikes which are driven by muscle force, specifically derailleur gearshifts, hub gearshifts and bicycle gearshifts.
The derailleur gearshift has not changed significantly in the last decades. In this context, a chain transmits the driving force from a foot pedal to the rear axle of the bicycle, wherein a sprocket cassette which is mounted on the rear axle is mounted with up to ten sprockets, between which sprockets it is possible to shift to and fro by means of a shifting mechanism for guiding the chain, which mechanism is attached to the frame. Furthermore, most bicycles are additionally equipped with a shifting means on the chainwheel of the bottom bracket. Here, up to three chainwheels are attached to the foot pedal, and it is possible to shift to and fro between said chainwheels by means of a derailer which is attached to the frame. Such derailer gearshifts offer up to thirty gearspeeds, but due to the system a large number of gearspeeds are redundant, and some gearspeeds cannot be used, or can only be used to a restricted degree, as a result of high frictional losses due to a diagonal course of the chain.
A disadvantage with the principle of the derailer gearshift is not only the large number of redundant gearspeeds and the frictional losses but also the fact that the components are exposed and are therefore subject directly to environmental influences such as water and dirt and can very easily be damaged by shocks.
The second type of commercially available bicycle gearshift is the hub gearshift. In contrast to the derailer gearshift, this is understood to be a gearshift which is installed in the hub housing of the rear axle. A hub gearshift usually does not have any shifting components which are located on the outside and is therefore insensitive to shocks and subject to a lesser degree to the environmental influences than the derailer gearshift. A hub gearshift such as is known, for example, from DE 197 20 794 A1 can currently implement up to 14 gearspeeds. A disadvantage with the principle of the hub gearshift in the rear axle is that the weight of the rotating masses is increased and, in the case of bicycles which have rear wheel suspension, the non-suspended mass is increased considered relative to the overall weight. In addition, the center of gravity of the bicycle is displaced in the direction of the rear axle, which has an unfavorable effect on the riding properties of the bicycle, in particular in the case of mountain bikes with rear wheel suspension.
Such a hub gearshift is known, for example, from EP 0 383 350 B1, in which two planetary gear mechanisms are arranged coaxially with respect to a hub which is fixed to the housing, wherein the input shaft can be connected to planetary carriers, and the sun gears of the planetary gear mechanisms can be connected in a rotationally fixed fashion via a rotatable shifting device to the hub which is fixed to the housing, in order to implement different transmission ratios of the transmission as a whole. A disadvantage with this transmission is that the transmission as a whole is complicated and accordingly is, on the one hand, costly to manufacture and, on the other hand, has, due to the large number of components, a large weight with, at the same time, small number of gearspeeds which can be implemented.
The third variant of the bicycle gearshift is the bicycle gear mechanism or bottom bracket gear mechanism which is mounted in the region of the bottom bracket. This type of bicycle gearshift is not widespread, or is only found rarely, in commercially available bicycles. In general, such bicycle gear mechanisms have the advantage over conventional derailer gearshifts or hub gearshifts that they do not have any exposed components and accordingly are protected against shocks and environmental influences, and on the other hand they displace the center of gravity of the bicycle into the center, in which case at the same time the sum of the non-suspended mass is reduced. This is of particular advantage in the sport of mounting biking. A technical requirement in such bicycle gear mechanisms is to implement a compact design accompanied at the same time by a large number of shiftable gearspeeds.
U.S. Pat. No. 5,924,950 A discloses a bicycle gear mechanism having an input shaft on which a multiplicity of driving gears are mounted, and a countershaft on which a corresponding number of shiftable driven gears is mounted. The shiftable gears of the countershaft are shifted by means of a plurality of axially displaceable shifting pins and freewheels which are arranged in the countershaft, wherein the countershaft is connected via a planetary gear mechanism to a sprocket as an output element of the bicycle gear mechanism. The sprocket is connected via a clutch to the sun gear of the planetary gear mechanism, and the ring gear of the planetary gear mechanism can be braked by means of a Bowden cable. Fourteen gearspeeds can be implemented by means of this bicycle gear mechanism. A disadvantage of this system is the axially large design and the comparatively small number of fourteen implementable gearspeeds.
In addition, WO 2008/089932 A1 discloses a transmission unit for bicycles, in which transmission units a large number of gearspeeds can be implemented by means of two countershafts and a further partial transmission by multiplying the individual gearspeeds of the two partial transmissions, and at the same time a compact design can be implemented. A disadvantage with this transmission unit is that, in order to shift the idler gears, a camshaft is displaced axially and the transmission therefore requires a large amount of space in the axial direction.